1. Field of the Invention
The present invention relates to a heat dissipation device, especially to a heat dissipation device that provides stable control signal to maintain stability of a rotation speed of a fan module of the heat dissipation device.
2. Description of the Related Art
A central processing unit (CPU) executes computer programs. When processing lots of data, the CPU generates large amounts of heat and requires effective cooling solutions. Usually a fan module is mounted upon the CPU to keep the CPU cool.
Since the CPU and the fan module are often disposed inside a computer, users cannot see whether the fan module is working properly or not. To solve the problem, with reference to FIG. 4, a motherboard (40) of a computer has a hardware monitor chip (42) that generates PWM (Pulse-width modulation) signals to control rotation speed of a fan module (30). The motherboard (40) has a main controller (41), such as a south-bridge chip, which gives out control signals to the hardware monitor chip (42). The hardware monitor chip (42) then changes pulse width of the PWM signals accordingly.
The fan module (30) has a motor coil (33), a connecting interface (32), a rotation speed meter (34) and a PWM driving circuit (31). The motor coil (33) may be a stator coil or a rotor coil depending on design requirements of the fan module (30). The rotation speed meter (34) may be implemented as an encoder. The connecting interface (32) includes a PWM pin (PWM), a rotation speed detect pin (Tach Out), a power supply pin (Vcc) and a ground pin (GND). The power supply pin (Vcc) and the ground pin (GND) are connected to the motherboard (40) to derive operation power from a power supply of a computer. The PWM pin (PWM) and the rotation speed detect pin (Tach Out) are connected to the hardware monitor chip (42). The PWM driving circuit (31) is electrically connected to the motor coil (33) and the PWM pin.
When receiving PWM signals from the hardware monitor chip (42) via the PWM pin, the PWM driving circuit (31) accordingly controls current magnitude and current direction of the motor coil (33) to drive the fan module (30). Meanwhile, the hardware monitor chip (42) receives the present rotation speed signal from the rotation speed detect pin (Tach Out) and accordingly computes the actual rotation speed of the fan module (30) as a basis for adjusting the rotation speed.
However, a large computer system often requires multiple fan modules to dissipate heat. With the foregoing method, communication between the hardware monitor chip (42) and the fan module (30) is unidirectional. The hardware monitor chip (42) gives out PWM signals to the fan module (30), but the fan module (30) does not automatically reply whether the received PWM signals are correct or not. Furthermore, in order to drive the fan modules (30), conductive path for transmitting a PWM signal is so long that the PWM signals are easily disturbed by outer noises. Once the PWM signal is disturbed with noises, the fan modules (30) may not work with a stable rotation speed and the main controller (41) cannot detect and react to such situation.
To overcome the shortcomings, the present invention provides a heat dissipation device to mitigate or obviate the aforementioned problems.